These were Maranoa (56 per cent "no"), Kennedy (53 per cent) and Groom (51 per cent) - meaning Mr Littleproud and Mr Katter voted in line with the wishes of the majority of their constituents.

Mr Pitt's constituents in Hinkler, which covers the city of Bundaberg, voted slightly higher in favour of legalising same-sex marriage (49 per cent "no"), but it was still in the top 20 (out of 150) in the nation for the "no" vote.

He joined those voting "no".

LNP member for Groom John McVeigh was in the chamber and voted yes, which was not in line with the slight majority of his constituents who voted "no".

Speaking during the debate on Wednesday night, Mr Katter said no one seemed to get married in north Queensland.

"I can't remember the last time I found a couple getting married, so mate, we can't get the heteros to marry - you've got absolutely no hope of getting that other mob to marry," he said.

On Tuesday, Mr Pitt said a difference of just 551 primary votes would have changed the result from a majority "yes" to "no" in his electorate of Hinkler, with 23,000 constituents not returning their ballots.

Mr Pitt said he had supported the "no" case consistently throughout the two elections, and supported the postal survey.

"I held a consistent position throughout the public debate that I would vote 'no' in the postal survey," he said.

"However, I did not engage in pushing either side of the debate during that survey, because my view was quite simply that my constituents would make up their own minds."

Mr Pitt said he was raised in the Catholic faith and would support the proposed amendments for religious freedoms, which ultimately failed.

"I think it's critical that the 4 million Australians who did vote 'no' not only are represented in this place, but have their views protected in this bill," he said.

"So my final decision to support or otherwise this bill will not be a reflection of the survey results or a reflection of those who've successfully lobbied for a change to the Marriage Act, because the change will take place.

"It will be simply a reflection on the bill which is before the House and a view as to whether it does or does not adequately address the concerns of many in my electorate.

"I'm aware of the opportunity to abstain from the vote but I'm one of those in this place who believe you should have the courage of your convictions."

During the debate, Dr McVeigh said he "supported the traditional definition of marriage" and would be supporting religious freedom amendments, although he did not want to frustrate the progress of the bill.

He said his Toowoomba electorate included representatives from the LGBTIQ community and Australian Christian Lobby managing director Lyle Shelton.

"I support very strongly, above all else, the view that respect for differing positions on the result of the survey on the question of same-sex marriage must be maintained, and that such an approach will ultimately ensure that this is, indeed, a unifying moment for our country," he said.